Conventional trailer hitches for light weight automobile and truck type vehicles normally include a hitch plate or bar which is welded adjacent the rear bumper of the vehicle or on the rear bumper of the vehicle and to which a hitch ball may be selectively secured. There are a number of conventional sizes of hitch balls which may be utilized depending upon the hitch assembly which is incorporated with the trailer that is to be towed. One shortcoming in such conventional rear end hitch assemblies is that the amount of weight which may be pulled by the vehicle is limited by the weight or force of the load which acts vertically on the hitch assembly since the hitch ball is located at a point which is spaced rearward from the rear axle of the vehicle. With this type of assembly, an increased moment of force is induced about the rear axle thereby limiting the load which may be safely pulled by the vehicle without adversely effecting the weight distribution to the front wheels of the vehicle. Reducing the weight distribution on the front wheels can adversely affect steering and braking of the vehicle and can also affect traction in front wheel drive vehicles.
In order to overcome the foregoing problem, a system for mounting trailer hitches was developed which has been referred to as a “fifth wheel” type trailer hitch. The fifth wheel trailer hitch includes a hitch ball which is mounted over or slightly forward of the rear axle of a flat bed type vehicle and particularly pickup trucks. By positioning the hitch ball above or forward of the rear axle of the vehicle, the weight which the vehicle can tow is significantly increased over vehicles having the rear end type hitch assemblies. In order to allow the trailing vehicle to be connected to a fifth wheel type hitch, a “gooseneck” type extension is utilized on the towing arm of the trailing vehicle. The gooseneck is generally somewhat curved with the hitch portion being disposed at its forward end, with a central portion extending upwardly and over the rear of the pulling vehicle.
Although fifth wheel trailer hitch assemblies provide the added advantage of allowing a vehicle to safely tow a greater weight load, the placement of the trailer hitch ball along the cargo bed of the towing vehicle can adversely affect the normal use of the cargo bed when the vehicle is not being utilized to pull a trailer. In order to overcome this disadvantage, there have been a number of structures developed for allowing the trailer hitch ball to be either selectively removed, retracted, or reversed from its use position relative to the cargo bed of the towing vehicle.
Pickup trucks are typically constructed as a separate frame or chassis and body, the frame generally being formed by elongated beam type members and cross members from stock such as I-beams, tubes, or the like. More recently, pickup truck frames have been formed using “hydroforming” techniques. In a hydroforming process, an enclosed shape, such as tubular stock, is filled with a fluid, sealed at the opposite ends, then cold formed in a die to a more complex shape, including bends. The fluid prevents collapsing of the tube and maintains a desired cross sectional shape of the resulting tubular product. After forming, the fluid is drained from the hydroformed beam. For more details describing hydroforming processes, see U.S. Pat. Nos. 1,943,560 or 5,339,667.
Hydroforming techniques typically result in a structure of a desired shape which has a desired strength with a lighter weight, for a given volume of metal. This result is achieved in part by producing a frame member with reduced wall thickness. It has been customary to attach hitch assemblies to truck frame members by drilling holes in the walls or web of existing chassis frame members, positioning a hitch assembly mounting plate next to the frame member and threading a bolt through an opening in the mounting plate aligned with the hole bored into the chassis frame member. A nut on the bolt is then drawn down tight.
Due to the reduced wall thickness of hydroformed frame members, warranties covering hydroformed products, such as vehicle frames, often do not allow drilling additional holes or welding to such frames, beyond those that are originally designed for by the manufacturer. Additionally, there are limits to clamping pressures which may be applied to such hydroformed frame members particularly clamping forces applied across or perpendicular to the walls or web of the hydroformed frame members. For example, the forces exerted on the wall of a hydroformed frame member by the head of a bolt or a nut drawn toward each other when tightening a nut to bolt the hitch assembly base to the frame member may be sufficient to collapse the wall of the frame member thereby weakening the frame member. This presents problems in connecting conventional fifth wheel hitch structures to pickup trucks incorporating hydroformed frame members. What is needed is a fifth wheel hitch structure which can be securely attached to hydroformed frame members without the use of welds, additionally drilled holes, or excessive clamping pressures.